1. Field of the Invention
This invention relates to a process for accurately positioning a lead frame onto a ceramic chip carrier to permit wire bonding to the lead frame by means of automatic wire bonding machinery and also relates to the formation of a grounding pad positioned beneath the chip which is bonded simultaneously with the leads of the lead frame and is capable of passing gases therethrough during the bonding procedure.
2. Description of the Prior Art
In the formation of ceramic chip carriers, lead frames are normally bonded to the ceramic substrate with subsequent connections being made to the leads of the lead frame from appropriate pads on semiconductor chips secured to the ceramic substrate. These connections from the pads on the chip to the leads of the lead frame are made manually or by means of automatic wire bonding machinery or by mass-bonding techniques using "spider" tape. The automatic wire bonding machinery is normally computer operated on an x-y coordinate basis and it is therefore necessary that the leads of the lead frame be accurately positioned on the substrate so that wiring which is run from pads on the semiconductor chip to the appropriate lead on the lead frame.
In accrdance with some of the prior art, the entire lead frame was bonded to the ceramic substrate by well-known methods and the portions of the leads closely adjacent to the semiconductor device to which wire bonding was to take place would move relative to the semiconductor pads during the process of bonding the lead frame to the ceramic substrate. It is therefore readily apparent that the automatic wire bonding machines cannot be used with the types of prior art combinations of substrate and lead frame because bonding from appropriate pads of the semiconductor devices to the appropriate leads of the lead frame cannot be definitely predicted. It is therefore necessary that a lead frame be bonded to a ceramic substrate wherein the leads of the lead frame are accurately positioned on the substrate and maintain their position during and after the procedure of bonding the lead frame to the substrate. It is also desirable that ground pads be provided in the event ground potential is to be provided to the bottom surface of the semiconductor chip wherein the ground pad can remain securely bonded to the substrate.